Although the pathwasy of gene expression are understood in broad outline, the regulatory metabolism which controls growth and differentiation in animal cells remains largely obscure. The intent of this research program is to investigate this metabolism at several levels in order to contribute to an understanding of normal development and of the defective differentiation and uncontrolled growth which are associated with neoplasia. The major plan is to continue three ongoing and interrelated investigations: (1) Control of hemoglobin gene expression in Friend virus-induced erythroleukemia cells in tissue culture. These cell lines can be induced in vitro to synthesize hemoglobin and to simultaneously increase their production of virus particles. The possible causal interrelationships between differentiation, malignancy and virus formation will be analyzed by genetic, immunological, and biochemical methods. (2) Functions of "double-sized" hemoglobin messenger RNA. We have recently found that a large fraction (c.a., 30%) of the globin mRNA in rabbit reticulocyte polyribosomes has twice the molecular weight of the majority of globin mRNA. The question of whether this is a polycistronic mRNA simultaneously encoding two globin chains and/or precursor of the smaller sized mRNA will be analyzed by several methods. To ascribe either identity to this mRNA would be unprecedented and extremely important. (3) Phosphorylation of ribosomal proteins. We discovered in this laboratory that several of the ribosomal proteins in eukaryotic cells are phosphorylated. Cyclic AMP appears to control the phosphorylation of one of these proteins. Studies are proposed for analyzing the functions of this metabolism. The organizational plan is that project (1) will become increasingly central to this laboratory.